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golang defer執(zhí)行順序全面詳解

更新時(shí)間：2023年09月27日 11:19:09 作者：werbenhu

這篇文章主要為大家介紹了golang defer執(zhí)行順序全面詳解,有需要的朋友可以借鑒參考下,希望能夠有所幫助,祝大家多多進(jìn)步,早日升職加薪

defer的執(zhí)行順序

多個(gè)defer是一個(gè)棧的結(jié)構(gòu)，是先進(jìn)后出，下面這個(gè)代碼的輸出順序是CBA。

package main
import "fmt"
func main() {
    defer func1()
    defer func2()
    defer func3()
}
func func1() {
    fmt.Println("A")
}
func func2() {
    fmt.Println("B")
}
func func3() {
    fmt.Println("C")
}

defer和return的順序

先執(zhí)行return，再執(zhí)行defer。

package main
import "fmt"
func deferFunc() {
    fmt.Println("defer func called")
}
func returnFunc() int {
    fmt.Println("return func called")
    return 0
}
func returnAndDefer() int {
    defer deferFunc()
    return returnFunc()
}
func main() {
    returnAndDefer()
}
// output:
// return func called 
// defer func called

函數(shù)命名返回值遇見defer

package main
import "fmt"
func foo() (t int) {
    defer func() {
        t = t * 10
    }()
    return 1
}
func main() {
    fmt.Println(foo())
}
// output: 10

defer和panic

panic阻斷defer

import (
    "fmt"
)
func deferFn() {
    defer func() { fmt.Println("defer before panic 1") }()
    defer func() { fmt.Println("defer before panic 2") }()
    panic("exit")
    defer func() { fmt.Println("defer after panic") }()
}
func main() {
    deferFn()
    fmt.Println("main exit")
}
/*
output:
defer before panic 2
defer before panic 1
panic: exit
...
*/

defer里面的recover

defer在panic 后依然有效

package main
import (
    "fmt"
)
func deferFn() {
    defer func() {
        fmt.Println("defer before panic 1")
        if err := recover(); err != nil {
            fmt.Println(err)
        }
    }()
    defer func() { fmt.Println("defer before panic 2") }()
    panic("panic info")
    defer func() { fmt.Println("defer after panic") }()
}
func main() {
    deferFn()
    fmt.Println("main exit")
}
/*
output:
defer before panic 2
defer before panic 1
panic info
main exit
*/

defer中包含panic

panic僅有最后一個(gè)可以被revover捕獲

package main
import (
    "fmt"
)
func main() {
    defer func() {
        if err := recover(); err != nil {
            fmt.Println(err)
        } else {
            fmt.Println("defer call")
        }
    }()
    defer func() {
        panic("defer panic")
    }()
    panic("main panic")
}
// output: defer panic

defer中函數(shù)有參數(shù)和包含子函數(shù)

package main
import "fmt"
func foo(index int, value int) int {
    fmt.Println(index)
    return index
}
func main() {
    defer foo(1, foo(3, 0))
    defer foo(2, foo(4, 0))
}
// output: 3 4 2 1

測(cè)試練習(xí)

package main
import "fmt"
func DeferFunc1(i int) (t int) {
    t = i
    defer func() {
        t += 3
    }()
    return t
}
func DeferFunc2(i int) int {
    t := i
    defer func() {
        t += 3
    }()
    return t
}
func DeferFunc3(i int) (t int) {
    defer func() {
        t += i
    }()
    return 2
}
func DeferFunc4() (t int) {
    defer func(i int) {
        fmt.Println(i)
        fmt.Println(t)
    }(t)
    t = 1
    return 2
}
func main() {
    fmt.Println(DeferFunc1(1))
    fmt.Println(DeferFunc2(1))
    fmt.Println(DeferFunc3(1))
    DeferFunc4()
}

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